You and Your Genes Making It in a Tough Environment 2011 508

8/19/2019 You and Your Genes Making It in a Tough Environment 2011 508

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The National Institute of Environmental Health Sciences

Making it in a Tough Environment Making it in a Tough Environment


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your genes.

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Lots of things

in our homes and schools and workplaces — and in wild and natural places —

can cause harm sometimes. Why "sometimes"? The harm may depend on who you are —

as well as what you do, what you are exposed to, and when.

Big, muscular people look as if they canresist anything. But they can have allergiesor asthma, or be injured by chemicals, too.And the bigger they come, the more skin thesun can burn!

Most of us, for example, can get sunburnedon a bright day. Your reaction will begreater if you are outside, without muchon, for a long time. Your reaction will be

less if you cover your exposed skin with lotsof sun screen. How bad you burn can depend

on your age and previous exposure. (Babies andtoddlers need a lot more protection.) Finally, if

one or both of your parents burn very easily,they may have passed that sensitivity to you in


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Designer Genes — They’re the Boss

Genes are the instructions — the marching orders — that direct our

growth, what we look like and how we react to things in our

world, or environment.

Each human — whether infant, child, teen or adult — has thousands of pairs of these orders, or genes. They tell our bodies' cells what to be andhow to behave.

Do you remember transformer toys? You twisted them one way and theywere space ships. You twisted them another way and they became robotwarriors. Well, under the genes' orders, the cells become the ultimate in

transformer robots. The genes instruct our original dab of cells, as

they divide, to become different — muscle, bone, lung, or braincells, or part of a toe. As a result of what the cells become

and do, we grow. And we stand and run and catch footballsand dance — more or less with grace and skill.We breathe. We think!

Our genes, or instructions, are coded on short segmentsof a long chemical chain called DNA. It is in the centerof each cell of our bodies. Think of genes as information

bits paired along two spiraling strands of this chemical — like snap-together beads in twolong, connected strings of DNA.

Every human has the same number and set of genes, so you might think we would allbe exactly the same. But the genes themselves vary a lot or a little, just as peopledo — and as animals do. That's why we do. For example, everyone has apair of genes for eye color but one variation instructs the eyes to be

blue while other variations order green or brown.

The complete package of genesfor an animal — what makes a dog

a dog — is called its genome.These packages or genomes are whypeople give birth to babies, dogs topuppies, and cats to kittens.

Many of the genes in other animalsare similar to those in humans. After

all, people and animals, like ourdogs, all have to do certain things,

like digesting food, so we need asimilar gene for that. When weare loyal, frisky and bright-eyed — and tip over garbagecans — maybe it's thoseshared genes?!

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Where did you get your pairs of genes?You got your genes when your dad's sperm pierced your mom's egg. One gene from each pair of your mother'sgenes was already waiting in the human egg. Your father's sperm added one gene from each of his pair of genes.Your father's and your mother's genes paired with each other inside that fertilized egg cell from which youthen grew.

The original egg cell split and re-split, forming new cells for muscle, brain, skin, bone and all the rest of your body.These new cells came together (according to the genes' orders) and each new cell carried copies of the originalcell's genes. The result: Two copies (a pair) of every gene are found in each of the 100 trillion or so cells of yourbody. (That's a lotza mozzarella!)

The mix of genes you each got from your parents directs your growthto adulthood and old age. When you have children, you, in turn, pass acopy of one or the other of each pair of your genes to each of your

kids — but not always the same one of the pair. Your husband orwife will do the same. Each child is very likely to get a differentmix and be different from the others.

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Even brothers and sisters (unless they are identical twins) don't get thesame mix of genes from their parents. So, although they may have simi

lar noses or hair or height, their bodies in other ways will be differentand may react differently — less or more — to the sun, to tobacco,alcohol or to some chemicals in bug killers or other products at home,school or work.

Getting features from our parentsis called our heredity, the sum of our genes. But our genes

alone will not determine all things, like size. A child who issick for a long time or doesn't eat well, for example, may

not grow as tall as his or her parents.

The reverse can happen, too. Good nutrition, cleanair and water, vaccines and simple hand-washing can

prevent diseases and help a kid soar above shorterparents.

In such ways, the substances you touch andbreathe, and your personal habits and nutritionplay important roles. Along with your genes, thegood and bad things in your world help decide who

you are, how you feel and whether you get sickor stay well.

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The Gene’s Code for LifeWhile the English language has 26 letters, each gene's orders, orinstructions, are written in a chemical code of four. The code is madeup of chemical bases called adenine, thymine, guanine andcytosine. We call these A, T , G and C — the gene code's fourletters. Long lines, or sequences, of these chemicals permit each ofthe genes to have a different code that directs the making of adifferent protein. One gene = one code = one protein. The proteinscarry out the gene's instructions.

xSome Tyypos Along the Way

Mistakes can occur as the code is copied and re-copied whenthe cells divide. A substance in our environment can sometimesmake a mistake occur or prevent it from being corrected by thebody's "spell check." Sometimes this doesn't matter much, butsometimes it matters a lot.

CELL

NUCLEUS

CHROMOSOMES

Proteins —not just beans and a big, juicy

steak, but a key to all life.

There are thousands of proteins, each

made up mostly of carbon, oxygen, hydrogen and nitrogen. Proteins are found in animal muscle (steak) and skin, bone and all the

"stuff" of life, every cell of an animal or plant.They are also what make the body work: They

are necessary for the chemical reactions thatmake muscles flex, brains think and stomachs

produce digestive fluids.

Think of genes as the orders or plans for ahouse. (This house could be your body, your dog's body or your petunia plant.)

Picture the proteins as not only thenuts and bolts, plaster and con

crete, wood beams and floorsbut the workers that create

and assemble these thingsand set the furnace and

lights and gas stoveto working.

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One msimisplaced letter in the long-strung code of one gene can cause sickle cell anemia —a painful disorder in which the red blood cells have an odd shape like a sickle or crescent moon, instead of being round.The sickle shape makes it hard for the blood cells to get around in the blood vessels.

Another disease that is inherited in this direct way is cystic fibrosis.This is a disease in which mucus clogs the lungs.

Most diseases have aHow small are your genes?

cells.

When youstuff yourself into a pair of tight jeans, think that all of your gene

pairs are stuffed by the thounon-gene trigger.sands into 23 pairs of long capsules called chromosomesUnlike cystic fibrosis and sickle cell anemia, most diseases and disorders are— which are in every one of ournot caused just by "bad" genes but by bad genes along with one or more "bad"

Even chromosomes arethings from the world around us. One scientist makes it very simple: Heredity

invisible to the naked eye.loads the gun and environment pulls the trigger!When these paired chromo-

Here's an example: When you were just born, you were tested for a genetic somes have been stained,

disease that is influenced by your environment — in this case, what you eat. however, they can be seen

That disease is PKU, in which protein is not eliminated but builds up. under a very good magnifying microscope.

If certain protein foods are eaten, the brain will not fully develop. (One artificialsweetener has a warning that it contains this protein and should not be used by Here's some trivia

people with PKU.) that could win a prize

on a TV quiz:"Chromo" is a Greekword for "color" or"stain," and"some" (rhymeswith "home") isGreek forDNA GENE

deoxyribonucleic acid "body."

(de-ox-e-RYE-bo-new-CLAY-ic

ASS-id)

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While some cancers, heart disease and diabetes run in families and may be due to "bad" genes, other things are at work,too. Our environment, our care in using chemical products, our personal habits and our diet and exercise can be important. Did you eat your broccoli today? Drink your O.J.? (Eating at leastfive fruits and vegetables a day appears to reduce our risk of cancer.)

And remember that the natural substances we encounter can some

times change a gene. Scientists say that some of our genes weremodified by conditions hundreds of years ago and were passed to usfrom our great, great grandparents.

Today, the chemicals or X-rays we need and use also can affectgenes, especially if people are careless about how they handlethese things. Smoking causes changes in the genes ofour lungs and other places in the body. Such a poisoncan garble a gene's code. The poison can affect

the message that a gene sends to cells to tellthem what to do, how to assemble and howto grow. It can undermine the cell's wayof correcting mistakes that can occur inthe DNA — the chemical chain thatcarries our genes.

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What gene variationsmake peoplerespond

differently?Researchers are studyinghow different people respond differently toharmful substances. They have found thatcommon differences in genes can affect thehuman body's responses.

For example, some genes signal the making of

proteins called enzymes, in the lungs.Ordinarily these enzymes, or active substances,destroy some of the cancer-causing substancesin tobacco smoke. But researchers have founda gene variation that may reduce theseenzymes and make people more susceptibleto lung cancer.

a gene with a variationFinding

that can cause a disease canhelp in the design of drugs to

counter it. Some scientists also looktoward correcting some diseases by molecules the cells are made of. Variations of a gene may

substituting a "good" gene mean more — or less — production of an enzyme that protectsbefore a baby is born. against these changes.

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Something similar may happen in emphysema (em-fizz-ZEEM-a),a disease in which a person's lung tissue deteriorates and heor she has a hard time breathing. Tobacco smoke, solventsused in factories, and other chemicals and air pollutantscan produce changes in lung tissue and cells and even in the


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Learning more about these variations: At the National Institute of EnvironmentalHealth Sciences, researchers want to find out more about these variations in the genes that make us more, or less,sensitive to the substances around us. To do this, they have developed a project called the "Environmental GenomeProject" with other parts of the National Institutes of Health.

The Environmental Genome Project meshes with the Human Genome Project,

which mapped every one of the genes in humans — the whole instruction bookfor the "human being."

The newer, "Environmental Genome Project" looks at genes that havealready been located. These particular genes have been shown to play arole in how we react to environmental substances. Scientists want to seehow these genes differ in different people, what percentage of us havewhich variations and what these variations mean in terms of our reactions.

These are not genes that give clear orders for a disease, regardless of other

A few people may have avariation that makes them very

resistant to a chemical.

A few may have a variationthat gives them a high chance of being

hurt by the same substance.

Most of us may be somewhere

in between.factors. Instead, these genes determine our weakness or strength in the face ofvarious metals, natural and human-made chemicals, radiation andsuch. They are called "susceptibility genes."

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The scientists in this project hope to discover: Are the people with such-and-such a gene variation more likely to beharmed by a chemical? Are the people with a different variation less at risk? How many people have this variation?How many have another?

The Environmental Genome Project will help answer the "Why me?" question. A smoker told he has developed a fatallung cancer asks this question because he knows of people who smoked as much and may have a hacking cough or

breathlessness but do not have lung cancer.Or perhaps you and your brother Joe work at a job around smoke or chemicals or smelly glues. Why might one of yoube hurt and the other not?

To find out how many of us have gene variations that protect us or, in other cases, make us susceptible, scientists testblood samples from several hundred volunteers representing the American people as a whole. The blood is tested forvariations in as many genes as the scientists are studying.

Tomorrow —In the future, will doctors give you a list of foods, chemicals, metals or other substances toavoid, based on how you react to them? Someday, very probably!

Most likely, the information will help you avoid some natural hazards you're susceptible to, much as people who aren'tstrong swimmers try to stay out of deep water, or people with diabetes avoid sugar. And industry and unions along withstate and federal regulators will have information to ensure that even those of us who react the most will be protected.

One way or another, we should gain a much better idea of which of us is at most risk — and what precautions need to betaken to best protect us.

This knowledge may help us prevent — or avoid — a lot of disease and disability,producing a better, safer future for us all.

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The National Institute of Environmental Health Sciences

The National Institute of Environmental Health Sciences has two big jobs:

1. Our scientists look for things in our world that may hurt our health.They discover what harm these substances can do and how we can getrid of these poisons or avoid them.

2. These scientists study how we react to these harmful things:Are we sensitive or resistant? Do you and I respond the same?Many of the differences between people are due to our genes.

Work involving genes is underway at many other institutes of the National

Institutes of Health, particularly at the National Human Genome ResearchInstitute (www.nhgri.nih.gov).

NIEHS/NIH Publication #98-4367

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICESNational Institutes of Health

National Institute of Environmental Health Sciences

www.niehs.nih.gov

A Special Thanks to J. Carl Barrett Publication Art: Susan Spangler

You and Your Genes Making It in a Tough Environment 2011 508

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